Add QPDFObjectHandle::getUniqueResourceName

2 files changed, 27 insertions, 23 deletions

diff --git a/libqpdf/QPDFObjectHandle.cc b/libqpdf/QPDFObjectHandle.cc
index b802a55c..4e77bbaa 100644
--- a/libqpdf/QPDFObjectHandle.cc
+++ b/libqpdf/QPDFObjectHandle.cc
@@ -931,6 +931,30 @@ QPDFObjectHandle::getResourceNames()
     return result;
 }
 
+std::string
+QPDFObjectHandle::getUniqueResourceName(std::string const& prefix,
+                                        int& min_suffix)
+{
+    std::set<std::string> names = getResourceNames();
+    int max_suffix = min_suffix + names.size();
+    while (min_suffix <= max_suffix)
+    {
+        std::string candidate = prefix + QUtil::int_to_string(min_suffix);
+        if (names.count(candidate) == 0)
+        {
+            return candidate;
+        }
+        // Increment after return; min_suffix should be the value
+        // used, not the next value.
+        ++min_suffix;
+    }
+    // This could only happen if there is a coding error.
+    // The number of candidates we test is more than the
+    // number of keys we're checking against.
+    throw std::logic_error("unable to find unconflicting name in"
+                           " QPDFObjectHandle::getUniqueResourceName");
+}
+
 // Indirect object accessors
 QPDF*
 QPDFObjectHandle::getOwningQPDF()
diff --git a/libqpdf/QPDFPageDocumentHelper.cc b/libqpdf/QPDFPageDocumentHelper.cc
index 3eec789b..58d6ed22 100644
--- a/libqpdf/QPDFPageDocumentHelper.cc
+++ b/libqpdf/QPDFPageDocumentHelper.cc
@@ -155,35 +155,15 @@ QPDFPageDocumentHelper::flattenAnnotationsForPage(
             {
                 QTC::TC("qpdf", "QPDFPageDocumentHelper non-widget annotation");
             }
-            std::set<std::string> names = resources.getResourceNames();
-            std::string name;
-            int max_fx = next_fx + names.size() + 1;
-            while (next_fx <= max_fx)
-            {
-                std::string candidate = "/Fxo" + QUtil::int_to_string(next_fx);
-                if (names.count(candidate) == 0)
-                {
-                    name = candidate;
-                    break;
-                }
-                ++next_fx;
-            }
-            if (name.empty())
-            {
-                // This could only happen if there is a coding error.
-                // The number of candidates we test is more than the
-                // number of keys we're checking against.
-                name = "/FxConflict";
-            }
+            std::string name = resources.getUniqueResourceName(
+                "/Fxo", next_fx);
             std::string content = aoh.getPageContentForAppearance(
                 name, rotate, required_flags, forbidden_flags);
             if (! content.empty())
             {
                 resources.mergeResources(
-                    QPDFObjectHandle::parse(
-                        "<< /XObject << " + name + " null >> >>"));
+                    QPDFObjectHandle::parse("<< /XObject << >> >>"));
                 resources.getKey("/XObject").replaceKey(name, as);
-                names.insert(name);
                 ++next_fx;
             }
             new_content += content;